Decorative laminates are well known articles of commerce which have been produced for many years. They can be used for a wide variety of table, counter, desk top and wall surfaces.
Conventional high-pressure decorative laminates are usually composed of a laminated supporting core, an absorbent print-barrier sheet and an overlay-protective sheet. The core is conventionally composed of a plurality of inexpensive kraft paper sheets, impregnated with a phenolic resin. The print sheet, which is placed on top of the core, is primarily used to supply the decorative effect to the laminate, be it a wood grain, marble, solid color or patterned effect.
The print sheet is conventionally made of expensive, smooth-surfaced, highly absorbent, heavy basis weight, pure grade regenerated alpha cellulose paper, loaded with costly fillers and impregnated with melamine-formaldehyde resin. The print sheet secondarily acts to absorb some of the phenolic resin leakage from the core during laminating. The print sheet also acts as a barrier sheet, where the melamine resin in the middle of the sheet, blocks further bleeding of phenolic resin from the core layer during high pressure laminating, and imparts color stability. The fillers impart an opacifying effect, to mask the dark color of the phenolic resin in the kraft paper core.
In the case of a multicolored wood grain laminate, having, for example, a distressed or weatherbeaten effect, three or perhaps four separate printings on the print sheet may be required. For each variation in shade, a different color print sheet may be necessary. This leads to necessitating a large stock of print sheet inventory, to the point that it has become an unmanageable burden on the laminating industry.
Because of the wear to which horizontal surfaces or outdoor vertical surfaces are subjected, a protective overlay sheet is conventionally applied over the print sheet. The overlay is conventionally made of pure grade paper, impregnated with a very high loading of melamine-formaldehyde resin. Because of the interface between the overlay and patterned print sheet, the decorative pattern, especially of fine wood grains, is not always as distinct as may be desired.
Arledter, in U.S. Pat. No. 2,816,851, attempted to solve pattern sharpness and phenolic resin bleeding problems, by printing the reverse side of an overlay sheet with a decorative design, such as a wood grain pattern. There, the overlay sheet had a special construction, and was impregnated with a melamine-formaldehyde resin. The overlay was used in conjunction with an unprinted, print sheet barrier paper, loaded with opacifying fillers, and impregnated with melamine-formaldehyde resin. The overlay sheet contained 50 weight percent pure grade cellulose fibers and 50 weight percent of a combination of rayon and glass fibers. This construction still retained the expensive filled barrier, required an expensive combination overlay, and did not solve inventory problems.
What is needed in the industry is a method of making a high pressure, patterned, decorative laminate, using an inexpensive overlay-print barrier sheet combination in conjunction with a minimal amount of expensive paper and filler, and utilizing at most a two resin system.